This invention relates to a method of manufacturing ink jet heads, and in particular, to a method of manufacturing ink jet heads wherein relative deviation of elongation owing to heating at the time the nozzle plate and the main body of the actuator are bonded together is prevented.
Heretofore, for a method of manufacturing ink jet heads, it was proposed and has been put into practice a method in which holes were made from the outside (front side) in the nozzle plate by a laser beam after it was bonded to the actuator. On the other hand, from the viewpoint of ink jetting characteristics (ink jetting direction, jetting amount, failure in jetting due to the suction of air after jetting, smudging and wetting on the outer surface of the nozzle plate, etc.), it is known that the shape of the nozzle holes having a structure tapering off towards the outside from the ink room is desirable. In the method in which holes were made from the outside (front side) of the nozzle plate, a complicated process was required for making the above-mentioned shape of the nozzle holes, which raised a problem in accuracy and productivity.
On the other hand, it is proposed a method wherein holes are made from the side of the ink room (rear side) of the actuator by a laser beam after the nozzle plate is bonded to the actuator. However, this method cannot be practiced for an ink jet head having the closed rear side although it depends on the type of its actuator; further, even for an ink jet head having the open rear side, when the depth of the actuator is large, it has been produced a problem that the laser beam was intercepted by partition walls of the channel grooves. Therefore, in the Japanese Patent No. 2,633,943, there is disclosed a technology in which nozzle holes are formed by the irradiation from the obliquely upward direction of the channel grooves. However, in this method, the irradiation is made from the obliquely upward direction, which makes the nozzles have an inclination (unable to be perpendicular to the nozzle plate), and the restriction in the working for obtaining proper ink jetting characteristics is very severe.
On the other hand, it is known a method in which nozzle hole working is applied to the nozzle plate in advance, and after that, the nozzle plate is bonded to the actuator with an adhesive.
For the material of the nozzle plate, resin materials such as polyimide have been used from the viewpoint of workability, durability, etc. It is known a method of manufacturing ink jet heads wherein nozzle holes are made beforehand in a resin material such as polyimide or the like and it is bonded to the actuator made of PZT (lead titanate-zirconate) by heating with a thermosetting adhesive to make the productivity good. However, in this method, it is required to make the adhesive be kept at a high temperature for the purpose of hardening the adhesive, and the nozzle plate and the actuator both come to be put under the same high-temperature environment. At this time, owing to the difference in the thermal expansion coefficient between the nozzle plate having a larger thermal expansion coefficient and the actuator having a smaller thermal expansion coefficient, the amount of elongation is different between the both, and they come to be bonded with the channel positions of the actuator deviated from the nozzle hole positions. This deviation is firmly held by the adhesive when the temperature drops to the normal temperature after the bonding; therefore, it is not removed, and as the result, there has been a problem that a positional deviation of the nozzle holes was inevitably produced.